<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>尝试修改h2标签的内容</title>
</head>
<body>
    <h2 id="test">尝试修改h2标签的内容</h2>
    <button onclick="update()">点击按钮修改h2标签中内容</button>
</body>
<script type="text/javascript">
    function update(){
        var h2 =document.getElementById('test')

        h2.innerHTML = '这是修改后的内容'
    }
</script>
</html>